Method for making an oxirane

ABSTRACT

Process for manufacturing an oxirane by reaction between an olefin and hydrogen peroxide in the presence of a catalyst and an organic diluent, according to which the hydrogen peroxide is an aqueous hydrogen peroxide solution obtained by extraction, with substantially pure water, of the mixture derived from the oxidation of at least one alkylanthrahydroquinone, without subsequent washing and/or purification treatment.

[0001] The invention relates to a process for manufacturing an oxiraneby reaction between an olefin and hydrogen peroxide in the presence of acatalyst and a diluent. The invention relates more particularly to aprocess for manufacturing 1,2-epoxypropane (or propylene oxide) byreaction between propylene and hydrogen peroxide.

[0002] It is known practice to manufacture propylene oxide byepoxidizing propylene using hydrogen peroxide in the presence of acatalyst of TS-1 type, as disclosed, for example, in patent applicationEP-A-0 230 949.

[0003] The hydrogen peroxide used is generally greatly freed fromorganic impurities. Thus, crude solutions of hydrogen peroxide (H₂O₂)arising from the extraction of a mixture derived from the oxidation ofat least one alkylanthrahydroquinone, generally undergo one or morewashing, extraction and/or distillation steps before being sold and/orused in synthetic processes. This is especially the case for the H₂O₂solutions used for the manufacture of oxiranes.

[0004] Patent application EP-A-0 549 013 relates to an integratedprocess for oxidizing organic substrates and for producing H₂O₂ via analkylanthraquinone (AO) process, which uses the water/alcohol mixtureused during the oxidation of the organic substrate as the solvent forextracting the H₂O₂ from the quinone shuttle. The Applicant has foundthat this process has several drawbacks:

[0005] the lack of flexibility of the overall process due to theinterdependence of each step of the synthesis (AO and oxidation);

[0006] the limitation of the alcohol content of the water/alcoholmixtures imposed by the extraction conditions, which penalizes thedegree of conversion of the H₂O₂ during the epoxidation reaction;

[0007] the difficulties of phase separation during extraction with awater/alcohol mixture;

[0008] the passage of large amounts of methanol into the quinoneshuttle, which, given the low flash point of methanol, results in anappreciable risk of explosion in the vapour phase during the step fromoxidation to the synthesis of the H₂O₂;

[0009] a large amount of quinones extracted in the water/alcoholmixture, which penalizes the economic viability of an industrial plant;and

[0010] the pollution of the quinone shuttle by by-products of theoxidation reaction.

[0011] Moreover, the propylene used in the known epoxidation reactionsis generally of relatively high purity, especially to avoid spuriousoxidation reactions of the impurities, and mainly for reasons of yieldand safety. Specifically, propane is the main impurity in propylene andit is reported in patent BE-A-1 001 884 that, in the presence of TS-1,hydrogen peroxide can oxidize an alkane.

[0012] In addition, in the case of propane, the oxidation productresulting therefrom is isopropanol. In the light of patent BE-A-1 001884, a person skilled in the art would have deduced that, in acontinuous process for producing propylene oxide with recycling of theorganic reaction diluent (generally methanol), and/or in a continuous orbatchwise process using a propane-rich source of propylene, isopropanolwould accumulate in the diluent and end up being converted into acetone,which is generally difficult to separate from this diluent. In thepresence of hydrogen peroxide, this acetone can form peroxides that areexplosive and also insoluble in organic medium, which further increasesthe explosion hazard following their precipitation. This type ofreasoning is applicable to any alkane oxidized in the presence of aperoxide compound and TS-1 and thus, to any source of olefin (recycledor otherwise) which is rich in alkane(s) and which would be intended foruse in an epoxidation reaction.

[0013] Thus, patents U.S. Pat. Nos. 5,599,955 and 5,599,956 disclose theuse of a substantially pure propylene, i.e. a propylene with a purity ofat least 90% and preferably of at least 98%, the main impurity of whichis propane.

[0014] Now, the various processes for synthesizing propylene (andolefins in general) generally lead to a propane content (or moregenerally a content of alkane(s)) which is appreciable, or even greaterthan that of the propylene, thus involving suitable separation and/orpurification processes. Patents U.S. Pat. Nos. 5,599,955 and 5,599,956mentioned above illustrate this problem.

[0015] In addition, various industrial processes using an olefin recyclethe unconverted fraction thereof, which is conventionally enriched inalkane(s). These processes are thus also liable to require a separationof the constituents prior to this recycling. Examples of such processesare the polymerization of olefins and their epoxidation.

[0016] A subject of the present invention is a process for manufacturingan oxirane which avoids at least one of the abovementioned drawbacks,while at the same time having an increased degree of conversion andbetter selectivity than that obtained using a purified extract.

[0017] The invention consequently relates to a process for manufacturingan oxirane by reaction between an olefin and hydrogen peroxide in the,presence of a catalyst and an organic diluent, according to which thehydrogen peroxide is an aqueous hydrogen peroxide solution obtained byextraction, with substantially pure water, of the mixture derived fromthe oxidation of at least one alkylanthrahydroquinone, withoutsubsequent washing and/or purification treatment.

[0018] Specifically, the Applicant has found, surprisingly, that thefact of using for the epoxidation reaction an H₂O₂ solution extractedwith water rather than with a water/alcohol mixture allows the degree ofconversion of this H₂O₂ to be increased. In addition, the fact of usingan unpurified extract allows again in selectivity compared with the useof a purified extract.

[0019] The processes for producing hydrogen peroxide usingalkylanthraquinone(s), or AO processes, are well known and are widelydocumented in the literature (see, for example, “Ullmann's Encyclopediaof Industrial Chemistry, Fifth Edition, 1989, Volume 3, p. 447-57”).They consist in subjecting a working solution of at least onealkylanthraquinone and/or of at least one tetrahydroalkylanthraquinoneto a hydrogenation step, in a diluent, to produce one or morealkylanthrahydroquinones and/or alkyltetrahydroanthrahydroquinones. Theworking solution leaving the hydrogenation step is then subjected to anoxidation with oxygen, air or oxygen-enriched air to give hydrogenperoxide and to reform the alkylanthraquinones and/oralkyltetrahydroanthraquinones. The hydrogen peroxide formed is thenseparated from the working solution by means of an extraction step.According to the present invention, this extraction is carried out usingsubstantially pure water. The working solution leaving the extractionstep is then recycled into the hydrogenation step in order to recommencethe hydrogen peroxide production cycle.

[0020] The term “alkylanthraquinones” is intended to denote, forexample, 9,10-anthraquinones substituted with at least one alkyl sidechain of linear or branched aliphatic type comprising at least onecarbon atom. These alkyl chains usually comprise less than 9 carbonatoms and preferably less than 6 carbon atoms. Examples of suchalkylanthraquinones are 2-ethylanthraquinone, 2-isopropylanthraquinone,2-sec- and 2-tert-butylanthraquinone, 1,3-, 2,3-, 1,4- and2,7-dimethylanthraquinone, and 2-iso- and 2-tert-amylanthraquinone, andmixtures of these quinones.

[0021] The expression “substantially pure water” is intended to denote awater containing less than 3% by weight of organic diluents, inparticular of alcohol(s), preferably less than 0.1% or even less than0.001% of these diluents. However, the extraction water mayadvantageously contain inorganic substances in a proportion of 0.001% byweight minimum, preferably 0.005% or even 0.01% minimum. However, thecontent of inorganic substances will not exceed 1% by weight, preferably0.5%, or even 0.1%. These inorganic substances are advantageouslysubstances which have a pH-regulating effect, such as acids and inparticular strong acids such as nitric acid or phosphoric acid, or saltsof such acids. These inorganic substances can also advantageously besubstances which have an H₂O₂-stabilizing effect, such as alkali metalsalts and alkaline-earth metal salts, and in particular sodium salts,such as sodium pyrophosphate. The extraction solution may thus comprisemetal cations (such as alkali metals or alkaline-earth metals, forinstance sodium) and/or anions such as phosphates, nitrates, etc. in lowcontents, generally less than 10 g/l, but greater than 0.01 g/l.

[0022] The H₂O₂ solution derived from the extraction, or crude H₂O₂solution, generally contains less than 50% by weight of H₂O₂, usuallyless than 40% of H₂O₂. It generally contains more than 5% by weight ofH₂O₂, usually more than 10%, in particular more than 20%, or even morethan 30%. It does not undergo any subsequent washing and/or purificationtreatment before being used in the epoxidation reaction. Consequently,it contains organic impurities (products of degradation of the quinoneshuttle) and inorganic impurities (cations and anions introduced by theextraction water, as well as those already present in the mixturederived from the oxidation of the alkylanthrahydroquinone(s)). Thesolution derived from the extraction may thus comprise organicimpurities expressed as TOC (total organic carbon concentration),defined according to ISO standard 8245, in a proportion of at least0.001 g/l, or even at least 0.01 g/l, or even at least 0.1 g/l, but notmore than 10 g/l, or even 1 g/l, or even 0.2 g/l. It may also containmetal cations (such as alkali metals or alkaline-earth metals, forinstance sodium) and/or anions such as phosphates, nitrates, etc. in lowcontents, generally less than or equal to 10 g/l, but greater than orequal to 0.01 g/l.

[0023] Before being used in the epoxidation reaction, the crudeH₂O₂solution may be diluted with water or any other solvent or liquiddiluent which has no adverse effect on the epoxidation reaction. Ingeneral, the aqueous solution used for the epoxidation contains at least5% by weight, usually at least 10% by weight, of H₂O₂, in particular atleast 20% by weight. It usually contains not more than 50% by weight ofperoxide compound, in particular 40% by weight.

[0024] The oxirane which may be prepared by the process according to theinvention is an organic compound comprising a group corresponding to thegeneral formula:

[0025] The oxirane generally contains from 3 to 10 carbon atoms,preferably from 3 to 6 carbon atoms. An oxirane which may be preparedadvantageously by the process according to the invention is1,2-epoxypropane.

[0026] The olefins which are suitable in the process according to theinvention generally contain from 3 to 10 carbon atoms and preferably 3to 6 carbon atoms. Propylene and butylene are particularly suitable.Propylene is preferred.

[0027] The catalysts used in the process according to the inventionadvantageously contain a zeolite, i.e. a solid containing silica whichhas a microporous crystal structure. The zeolite is advantageously freeof aluminium. It preferably contains titanium.

[0028] The zeolite which may be used in the process according to theinvention may have a crystal structure of ZSM-5, ZSM-11 or MCM-41 typeor of beta-zeolite type. Zeolites of ZSM-5 type are suitable. Those withan infrared adsorption band at about 950-960 cm⁻¹ are preferred.

[0029] The zeolites which are particularly suitable are the titaniumsilicalites. Those corresponding to the formula xTiO₂(1-x)SiO₂ in whichx is from 0.0001 to 0.5, preferably from 0.001 to 0.05, have goodperformance qualities. Materials of this type, known under the name TS-1and having a crystal structure of ZSM-5 type, give particularlyfavourable results.

[0030] The reaction medium according to the invention generallycomprises a liquid phase and a gaseous phase.

[0031] The organic diluents which may be used in the process accordingto the invention may be organic derivatives such as aliphatic alcohols,containing from 1 to 4 carbon atoms. Methanol may be mentioned by way ofexample. The content of diluent in the liquid phase of the reactionmedium is advantageously greater than 35% by weight, preferably greaterthan 60%, or even 75%. However, the content of diluent in the liquidphase of the reaction medium is generally less than 99% by weight,preferably less than 95%.

[0032] In one preferred variant of the process according to theinvention, the oxirane produced in the reaction medium may be separatedout by liquid-liquid extraction with a solvent as disclosed in patentapplication WO 99/14208 in the name of the Applicant.

[0033] The process according to the invention may be continuous orbatchwise. If it is continuous, the unreacted olefin may be recycledinto the reactor.

[0034] The reactor in which the process according to the invention takesplace may be fed with a solution arising directly from the aqueousextraction step of an AO process. In this case, the plant in which theprocess according to the invention takes place also incorporates a plantfor manufacturing the H₂O₂ solution according to an AO process. Such aplant and a process using it also constitute a subject of the presentinvention.

[0035] Alternatively, the solution may be stored and/or conveyed beforebeing -fed into the reactor, which is the case for the purifiedsolutions currently used.

[0036] In the process according to the invention, a gas which has noadverse effect on the epoxidation reaction may also be fed into thereactor. Specifically, in patent application WO 99/48883, the Applicanthas found that by introducing a gaseous compound into the reactionmedium at a flow rate which is sufficient to enable the oxirane producedto be entrained and removed from the reactor at the same time as thegaseous compound, the contact time between the oxirane produced and theepoxidation reaction medium is reduced. This thus avoids the formationof by-products and increases the selectivity of the epoxidation.

[0037] One advantageous embodiment of the process according to theinvention consists in introducing the gaseous phase into the reactor ata flow rate such that it not only entrains at least some of the oxiraneproduced, but also circulates the liquid phase in the reactor, inparticular when this reactor is a reactor of loop type. In this case,the gaseous phase is generally introduced into the reactor at a flowrate such that the molar ratio of the flow rate of this gaseous phase tothe H₂O₂ feed rate is at least 5, in particular at least 8, values of atleast 10 being common. The molar ratio of these flow rates is generallyless than or equal to 100, in particular less than or equal to 60,values of less than or equal to 40, or even 20, being common.

[0038] Any type of reactor may be used in the process according to theinvention, in particular a reactor of loop type. Reactors of loop typewith a bubble siphon, in which the circulation of the liquid and alsooptionally of the catalyst is obtained by bubbling a gas into one of thebranches, are suitable. This type of reactor is disclosed in theabovementioned patent application WO 99/48883.

[0039] In the process according to the invention, it may prove to beadvantageous to maintain the pH of the liquid phase during the reactionbetween the olefin and the H₂O₂ at a value of at least 4.8, inparticular of at least 5. The pH is advantageously less than or equal to6.5, in particular less than or equal to 6. Good results are obtainedwhen the pH is from 4.8 to 6.5, preferably from 5 to 6. The pH of theliquid phase during the epoxidation reaction may be controlled by addinga base. This base may be chosen from water-soluble strong bases whichmay be mentioned are NaOH and KOH. They may also be weak bases. The weakbases may be inorganic. Examples of weak inorganic bases which may bementioned are NH₄OH, Na₂CO₃, NaHCO₃, Na₂HPO₄, K₂CO₃, Li₂CO₃, KHCO₃,LiHCO₃ and K₂HPO₄. The weak bases may also be organic. Weak organicbases which may be suitable are the alkali metal or alkaline-earth metalsalts of carboxylic acids preferably containing from 1 to 10 carbonatoms. Sodium acetate may be mentioned by way of example. Weak basesgive good results. Weak organic bases are preferred. Sodium acetate isparticularly suitable.

[0040] The molar ratio between the amount of olefin used and the amountof H₂O₂ used is generally greater than or equal to 0.1, in particulargreater than or equal to 1, and preferably greater than 5. This molarratio is usually less than or equal to 100, in particular less than orequal to 50 and preferably less than or equal to 25.

[0041] In the process according to the invention, when it is performedcontinuously and in the presence of a zeolite, the H₂O₂ is generallyused in an amount of at least 0.005 mol per hour and per gram ofzeolite, in particular of at least 0.01 mol per hour and per gram ofzeolite. The amount of H₂O₂ is usually less than or equal to 2.5 mol perhour and per gram of zeolite, and in particular less than or equal to 1mol per hour and per gram of zeolite. Preference is shown for an amountof H₂O₂ of greater than or equal to 0.03 mol per hour and per gram ofzeolite and less than or equal to 0.1 mol per hour and per gram ofzeolite.

[0042] The reaction between the olefin and the H₂O₂ may be carried outin the presence of a salt such as a metal salt or an ammonium salt. Themetal may be chosen from alkali metals and alkaline-earth metals such aslithium, sodium, potassium, caesium, magnesium, calcium, strontium andbarium. The metal salts are advantageously halides, oxides, hydroxides,carbonates, sulphates and phosphates and organic acid salts such asacetates. The halides are generally fluorides, chlorides, bromides andiodides. Preference is shown for chlorides. The salt advantageously usedin the process according to the present invention is preferably analkali metal halide and advantageously sodium chloride. The amount ofmetal salt used is expressed as the content of metal ions or of ammoniumions arising from the salt relative to the amount of catalyst expressedin millimoles (mmol) of metal or of ammonium per gram of zeolite. Thiscontent may be greater than or equal to 10⁻⁴ mmol/g of zeolite and lessthan or equal to 10 mmol/g of zeolite. Advantageously, the metal saltcontent is greater than or equal to 10⁻³ mmol/g of zeolite and less thanor equal to 1 mmol/g of zeolite. Preference is shown for a content ofgreater than or equal to 10⁻² mmol/g of zeolite and less than or equalto 0.5 mmol/g of zeolite.

[0043] The temperature of the reaction between the olefin and the H₂O₂is advantageously greater than 35° C. to overcome the gradualdeactivation of the catalyst. It is advantageous to perform the reactionat a temperature of greater than or equal to 40° C. and preferredgreater than or equal to 45° C. A temperature of greater than or equalto 50° C. is most particularly preferred. However, the reactiontemperature is generally less than 100° C. and preferably less than 80°C. The temperature at which the olefin reacts with the H₂O₂ is generallybetween 40° C. and 100° C. and preferably between 45° C. and 80° C.

[0044] In the process according to the invention, the reaction betweenthe olefin and the H₂O₂ may take place at atmospheric pressure. It mayalso take place under pressure. Generally, this pressure does not exceed40 bar. A pressure of 20 bar is suitable in practice.

[0045] According to one particularly advantageous variant of the processaccording to the invention, the olefin is reacted with the hydrogenperoxide in the presence of the catalyst and the organic diluent in areactor in the liquid phase which is fed with hydrogen peroxide andorganic diluent as well as with a fluid comprising the olefin and atleast 10% by volume of alkane(s). The alkane content in the fluid ispreferably greater than 10% by volume.

[0046] This variant is advantageous since it upgrades the varioussources of olefins not freed of alkanes by using them to manufactureoxiranes, and since it reduces, surprisingly, during an oxidationreaction of an alkane with a hydrogen peroxide, the production ofalcohol and of ketone in the presence of an olefin, this even takingaccount of the dilution factor. Consequently, the danger ofprecipitation of explosive peroxides is markedly less than that whichwould be theoretically expected and can consequently be managed withease in a plant of industrial size.

[0047] One of the essential advantages of the advantageous variant liesin feeding a fluid containing at least 10% by volume of one or morealkane(s) into the reactor. The content of alkane(s) in this fluid mayin certain cases be at least equal to 20% by volume, or even 30%. Fluidscontaining at least 50% by volume of alkane(s) may also be used.However, it is not recommended to use fluids containing more than 95% byvolume of alkane(s), and it is even preferable to use fluids notcontaining more than 85% alkane(s).

[0048] The fluid usually contains more than 50% by volume of olefin, inparticular at least 60% by volume and preferably at least 70% by volume.The amount of hydrogen introduced into the epoxidation reactor isusually less than 5% of the volume of the fluid, and is preferably equalto 0%. The amount of oxygen introduced into the epoxidation reactor isgenerally less than 10% of the volume of the fluid.

[0049] The alkane(s) contained in the fluid according to the presentinvention generally contain(s) from 3 to 10 carbon atoms and preferably3 to 6 carbon atoms. Preferably, the alkane is linear and does notcontain any aromatic substitutents in particular. When the olefinaccording to the invention is propylene, the alkane(s) consist(s) mainlyof propane. Preferably, the alkane is not used as organic diluent forthe epoxidation reaction and is different from the organic diluent.

[0050] The process according to the advantageous variant may becontinuous or batchwise. If it is continuous, the fluid may be recycledinto the reactor after the reaction between the olefin and the hydrogenperoxide.

[0051] In a first case of the advantageous variant of the processaccording to the invention, the process is continuous and the fluid fedinto the reactor during the start of the process contains less than 10%by volume of alkane(s). During the process, the fluid is recycled intothe reactor after the reaction between the olefin and the hydrogenperoxide such that the fluid recycled is gradually enriched with alkane.The alkane content in the fluid thus reaches a value of at least 10% byvolume.

[0052] In a second case of the advantageous variant of the processaccording to the invention, this process is continuous or batchwise andthe fluid fed into the reactor during the start of the process alreadycontains at least 10% by volume of alkane(s).

[0053] Preferably, the fluid (comprising the olefin and the alkane(s))which is fed into the reactor is a gas. In this case, one particularembodiment of the advantageous variant of the process according to theinvention consists in introducing this gas into the reactor at a flowrate such that it not only entrains at least some of the oxiraneproduced, but also circulates the liquid phase in the reactor, inparticular when this reactor is a reactor of loop type. In this case,the gas is generally introduced into the reactor at a flow rate suchthat the molar ratio of the flow rate of this gas to the feed rate ofthe peroxide compound is at least 5, in particular at least 8, values ofat least 10 being common. The molar ratio of these flow rates isgenerally less than or equal to 100, in particular less than or equal to60, values of less than or equal to 40, or even 20, being common.

[0054] In the advantageous variant of the process according to theinvention, when it is performed continuously, preference is shown for anamount of hydrogen peroxide of greater than or equal to 0.03 mol perhour and per gram of zeolite and less than or equal to 0.25 mol per hourand per gram of zeolite.

[0055] In the advantageous variant of the process according to theinvention, the aqueous hydrogen peroxide solution usually contains-notmore than 70% by weight of peroxide compound, in particular 50% byweight.

[0056] The invention also relates to a process for manufacturing anoxirane, according to which an olefin is reacted, in a reactor in theliquid phase, with hydrogen peroxide in the presence of a catalyst andan organic diluent, in which the reactor is fed with hydrogen peroxideand with organic diluent, as well as with a fluid comprising the olefinand at least 10% by volume of alkane(s).

[0057] This other process of the invention corresponds to theadvantageous variant disclosed above when it is performed as suchwithout being combined with the first process of the invention whichuses an aqueous hydrogen peroxide solution obtained by extraction, usingsubstantially pure water, of the mixture derived from the oxidation ofat least one alkylanthrahydroquinone, without subsequent washing and/orpurification treatment.

[0058] The conditions under which this other process may be performedare identical to those of the first process except for the use of acrude hydrogen peroxide solution.

EXAMPLE 1 (According to the Invention) and Example 2C (Comparative)

[0059] A continuous reactor containing 5.25 g of TS-1 is maintained at35° C. and at atmospheric pressure and fed with 0.57 mol of H₂O₂/h,introduced in the form of an aqueous 40 wt % solution, with 4.75 mol ofmethanol/h and with 250 Nl/l (i.e. 11.2 mol/h) of propylene. The liquidand gaseous phases leaving are analysed to determine the proportions ofthe various organic products and also the degree of conversion of theH₂O₂.

[0060] The table below summarizes the results obtained after the tests,starting with a fresh TS-1 catalyst prepared according to the proceduresknown in the literature. 1 (invention) Crude extraction 2C (comparison)Example No. H₂O₂ Purified H₂O₂ Degree of conversion 76.7 76.0 of theH₂O₂ after running for 2 h Idem after 6 h 54 53 Selectivity* after 90.585.4 6 h

[0061] As is known, a gradual loss of activity of the catalyst isobserved, which is not affected by the quality of H₂O₂ used. Only theselectivity is favourably influenced in the presence of the crude H₂O₂.

[0062] The respective contents of anions and cations in these H₂O₂solutions should be noted: Content in mg/l Crude H₂O₂ Purified H₂O₂ Na26 2.3 Other cations (except H⁺) <0.3 <0.3 NO₃ 34 3.7 Phosphatesexpressed as P 28 1.4 TOC 172 69

Example 3 (According to the Invention) and Example 4C (Comparative)

[0063] The table below summarizes tests that are identical in allrespects to Example 1 and Example 2C, during a following cycle afterregeneration of the catalyst. This regeneration is obtained by passingair heated to 300° C. over the catalyst for 7 h. 3 (invention) 4C(comparison) Example No. Crude H₂O₂ Purified H₂O₂ Degree of conversion75.4 75.6 of the H₂O₂ after running for 2 h Idem after 6 h 53.5 54.3Selectivity** after 91.1 85.7 6 h

[0064] It is confirmed that the activities have, to within the accuracyof the measurements, remained identical and that the difference inselectivity is maintained.

EXAMPLE 5C (Comparative) and Example 6 (According to the Invention)

[0065] An H₂O₂ synthesis solution obtained after oxidizing aquinones/hydroquinones shuttle was extracted using a methanol/watermixture containing 52% by weight of methanol. This aqueous extract wasthen used in a propylene epoxidation test (Example 5C) and theperformance qualities obtained were compared with those of a similartest carried out with crude H₂O₂ at 40% by weight in water, obtainedfrom the extraction of the same shuttle with substantially pure water(Example 6). This shuttle contains 11.8 g/kg of H₂O₂.

[0066] The extraction with the water/alcohol mixture was carried out in4 steps:

[0067] A first extraction was carried out by treating 14 331 g ofshuttle (containing 169.1 g of H₂O₂ in total) with 1511 g of themethanol/water mixture. The methanol/water phase is denser than thestarting organic solution and separates out relatively quickly (in about15 min) to give 1085 g of extract. Its H₂O₂ concentration, determined byiodometry, is equal to 3.18 mol H₂O₂/kg, which corresponds to 3.45 molor 117.4 g of H₂O₂ (=69% of the total present).

[0068] A second extraction was carried out with 1522 g of the samemethanol/water mixture. The separation is less sharp. The separation ofthe phases is fairly slow: more than 1 h is required to be able toseparate the phases. In contrast with the first extraction, themethanol/water phase is less dense this time and consists of 1215 g ofextract. Its H₂O₂ concentration is equal to 0.833 mol/kg, which isequivalent to 1.012 mol or 34.4 g of H₂O₂. 90% of the total H₂O₂ arethus recovered in two extractions.

[0069] A third extraction was carried out with 1511 g of the samemethanol/water mixture. The same separation difficulty was encountered,with recovery of about 1446 g of methanol/water phase. Its H₂O₂concentration is equal to 0.244 mol/kg, which is equivalent to 0.353 molor 12.0 g of H₂O₂ (i.e. 96.9% of the total H₂O₂ in 3 extractions)

[0070] Finally, a fourth extraction was carried out with 1517 g of thesame methanol/water mixture. The same separation difficulty wasencountered, with recovery of about 1497 g of methanol/water phase. ItsH₂O₂ concentration is equal to 0.071 mol/kg, which is equivalent to0.106 mol or 3.6 g of H₂O₂ (i.e. 99.0% of the total H₂O₂ in 4extractions).

[0071] The 4 extracts were then mixed together, to give a methanol/watersolution containing 0.94 mol H₂O₂/kg (effectively confirmed bytitration) The methanol content determined by GC is in the region of 437g/kg.

[0072] The content of “useful” quinones (=which may be used to produceH₂O₂) lost in this phase is 0.020 g/kg of extract.

[0073] There has moreover clearly been passage of some of the methanolinto the quinone shuttle, as demonstrated by the differences between theweights of the methanol/water mixtures used and those of the collectedextracts (in particular for the first and second extractions). Themethanol content of the quinone shuttle, determined by GC, iseffectively in the region of 6.0% by weight.

[0074] The propylene (Pe) epoxidation tests were carried out in a plantof bubble siphon type under the following conditions: T: 55° C.; flowrate of Pe: 75 Nl/h; H₂O₂: 0.17 mol H₂O₂/h; concentration of H₂O₂ in thezero-conversion loop: 1.0 mol/kg; catalyst: 0.53 g of TS-1.

[0075] As regards Example 5, the introduction of the mixture alone ofthe four methanol/water extracts containing H₂O₂ into the bubble siphonplant would lead, following stripping, to a methanol-poor medium (conc.<440 g/kg). Consequently, additional methanol was added so as to keepits concentration in the loop at ≈440 g/kg, which corresponds to themethanol content of the reference test with crude H₂O₂ (Example 6).

[0076] The results obtained are given in the table below: Degree ofconversion of the H₂O₂ (%) 2 h 3 h 4 h 5 h 6 h 7 h 24 h 25 h 26 h Ex. 5C30.4 20.7 18.6 15.3 12.6 10.4  8.7  8.4  8.1 Ex. 6 33.3 25.5 24.4 20.420.1 19.6 17.5 18.4 17.2

EXAMPLES 7 to 9

[0077] Propylene oxide was manufactured in a bubble siphon reactor asdisclosed in patent application WO 99/48883, by reaction betweenpropylene and hydrogen peroxide in the presence of methanol and ofcatalyst TS-1 used in the form of beads 0.5 mm in diameter.

[0078] The tests were carried out at a temperature of 55° C., with acontinuous feed of hydrogen peroxide at a flow rate of 0.17 mol/h. Thetotal flow rate of gas is 75 Nl/h (i.e. 3.3 mol/h). The initial H₂O₂concentration in the zero-conversion loop was 1.5 mol/kg. The amount ofcatalyst used was 4.5 g of beads containing 1.5 g of TS-1.

[0079] In Example 1, a mixture containing 75% “polymer-grade” propylene(98% propylene and 0.3% propane) and 25% propane (molar %) was used; inExample 2, 100% “polymer grade” propylene was used, and in Example 3, amixture containing 75% “polymer grade” propylene and 25% nitrogen wasused.

[0080] The results obtained are given in the table below.

[0081] The selectivity towards propylene oxide is given by the molarratio, expressed as a percentage, between the amount of propylene oxideobtained divided by the sum of all the C3 organic products formed.Degree of conversion of H₂O₂ (%) Selectivity 5 h 6 h 7 h 5 h Example 757.4 55.3 52.6 85.8 Example 8 67.2 64.0 61.7 84.5 Example 9 59.1 53.351.2 85.9

[0082] The isopropanol production measured after 5 h is 0.007 mmol/h forExample 1. There is no detectable trace of isopropanol in Tests 2 and 3.

EXAMPLE 10

[0083] A test under conditions identical to those of Examples 7 to 9above was carried out with pure propane. The isopropanol productionmeasured after 5 h is 0.11 mmol/h, i.e. a factor of 16 relative toExample 1. There is also formation of 0.04 mmol/h of acetone. The H₂O₂conversion is very low, i.e. 1% after 5 h.

1. Process for manufacturing an oxirane by reaction between an olefinand hydrogen peroxide in the presence of a catalyst and an organicdiluent, according to which the hydrogen peroxide is an aqueous hydrogenperoxide solution obtained by extraction, with substantially pure water,of the mixture derived from the oxidation of at least onealkylanthrahydroquinone, without subsequent washing and/or purificationtreatment.
 2. Process according to claim 1, in which the oxirane is1,2-epoxypropane and the olefin is propylene.
 3. Process according toclaim 1 or 2, in which the extraction water contains less than 3% byweight of organic diluents, in particular of alcohol(s).
 4. Processaccording to any one of the preceding claims, in which the H₂O₂ solutionobtained by extraction contains at least 0.001 g/l and not more than 10g/l of organic impurities expressed as TOC.
 5. Process according to anyone of the preceding claims, in which the H₂O₂ solution obtained byextraction contains metal cations (such as alkali metals oralkaline-earth metals, for instance sodium) and anions (such asphosphates or nitrates) in contents of greater than or equal to 0.01 g/land less than or equal to 10 g/l.
 6. Process according to any one of thepreceding claims, in which the H₂O₂ solution obtained by extractioncomprises at least 5% by weight and not more than 50% by weight ofhydrogen peroxide.
 7. Process according to any one of the precedingclaims, in which the catalyst is titanium silicalite, preferably of TS-1type, with a crystal structure of ZSM-5 type, and the diluent ismethanol.
 8. Process according to any one of the preceding claims, inwhich the reaction medium comprises a liquid phase and a gaseous phase,and in which the content of organic diluent in the liquid phase isgreater than 35% by weight.
 9. Process according to any one of thepreceding claims, according to which the olefin is reacted with thehydrogen peroxide in the presence of the catalyst and the organicdiluent in a reactor in the liquid phase, in which the reactor is fedwith hydrogen peroxide and diluent as well as with a fluid comprisingthe olefin and at least 10% by volume of alkane(s).
 10. Processaccording to claim 9, in which the content of alkane(s) in the fluid isat least equal to 20% by volume, preferably 30%.
 11. Process accordingto claim 9 or 10, in which the content of alkane(s) in the fluid is lessthan or equal to 95% by volume, preferably less than or equal to 85%.12. Process according to any one of claims 9 to 11, which is acontinuous process in which the fluid fed into the reactor during thestart of the process contains less than 10% by volume of alkane(s), but,after recycling it into the reactor after the reaction between theolefin and the peroxide compound, it is gradually enriched withalkane(s) until it reaches a value of at least 10% by volume. 13.Process according to any one of claims 9 to 11, in which the fluid whichfeeds the reactor during the start of the process contains at least 10%by volume of alkane(s).
 14. Process according to any one of claims 9 to13, in which the reactor is a loop reactor, the fluid comprising theolefin and the alkane(s) is a gas and the molar ratio of the flow rateof this gas to the feed rate of the peroxide compound is greater than orequal to 5, preferably greater than or equal to
 10. 15. Processaccording to any one of claims 9 to 14, in which the oxirane is1,2-epoxypropane, the olefin is propylene and the alkane is propane. 16.Plant for carrying out a process according to claims 1 to 15, whichincorporates a plant for manufacturing H₂O₂ solution according to an AOprocess.
 17. Integrated process for manufacturing H₂O₂ according to anAO process and for manufacturing oxirane by reaction between an olefinand H₂O₂, using the plant according to claim 16.